1. Technical Field
This invention relates to railway vehicles and trucks therefor. More particularly, this invention relates to a means for absorbing lateral loads between a bearing supported axle and a rail vehicle truck.
2. Background
Conventional railway truck designs comprising a pair of laterally-spaced side frames, at least one transom, and a plurality of axle and wheel sets extending transversely there between have become the standard in many railway industry applications. Problems encountered with these conventional rail trucks include the tendency for the wheel sets to traverse curves in a non-radial orientation and with much wheel flange to rail rubbing contact. Furthermore, the wheel sets may tend to slide during negotiation of track curves. Such rubbing contact and wheel sliding result in undesirably high wheel and rail wear, and the flange rubbing in particular may produce a tendency for the wheel to climb the rail. Improper wheel set tracking in curves may also result in truck misalignment.
Additionally, curved and imperfect track and imperfect wheels impose lateral forces on the wheel sets, tending to displace them laterally off the truck's centerline. When a rail vehicle truck having a number of axles held parallel or in fixed relation to one another passes through a curve, the truck experiences "basic" lateral loading forces, known as curve negotiation forces, which are related to the frictional forces between the rails and wheels. These forces result from the fact that all wheels of the truck cannot line up tangent to the rails, especially with multiple axle trucks.
In addition to the "basic" lateral forces which occur even with theoretically perfect wheel and rail interaction, other dynamic lateral forces occur as a result of the inevitable imperfections and wear in the rail and wheels, and the wheels passing through switches and crossovers. These lateral forces are transmitted through the axle to the bearing and bearing housing supporting the axle on the truck, resulting in increased wear of the bearings and other truck components.
Other related problems occur when conventional trucks traverse straight, or tangent, runs of track. For example, a rigid wheel axis set, having conventional tapered conical wheels, when displaced laterally from the centerline of a run of straight track, executes two simultaneous motions; first, the wheel set moves toward the equilibrium (center) position under the influence of gravity, and secondly, the high side wheel, rolling on a larger diameter than the low side wheel, moves along the rail faster than its partner, causing the wheel set to yaw. Given the proper set of circumstances, this motion may become a sustained, harmonic oscillation known as hunting. The hunting tendency is transmitted to the truck and causes an oscillatory yawing motion of the truck about its center of rotation, resulting in additionally high truck component wheel and rail wear.
The problems associated with wheel sets traversing curves in a non-radial orientation have been recognized in the prior art and a variety of self-steering railway truck designs have been devised which purport to allow wheel sets to track without sliding and without undue flange rubbing during negotiation of curves, and with minimal adverse consequences resulting from hunting. These designs typically interconnect diagonally opposite wheels on the end axles of a truck so that an opposite rotation, or yaw, of one truck axle is induced in response to the yawing of another truck axle when the truck is encountering a curve. Such a self-steering railway truck design is shown in the patent to Goding, U.S. Pat. No. 4,765,250.
The axles of a rail vehicle truck are rotatably supported parallel to one another in the truck frame by bearing assemblies which are mounted to the truck frame generally within bearing housings which fit between members of the truck frame known as pedestals. Relative, generally longitudinal motion between the bearing housing and respective pedestals is necessary in order to permit the axles to yaw pursuant to the self-steering action of the truck. Furthermore, the pedestals must be free to slide vertically up and down relative to their respective bearing housing to permit frame mounted cushioning springs to absorb shock that would otherwise be transmitted from the wheel sets through the bearings to the truck frame.
The problems associated with lateral thrust loads and lateral displacement of the wheel sets in relation to the frame members during negotiation of curves have been addressed in a variety of ways. For example, it is known to provide rubber cushioning members internal to a bearing housing, as in Janeway, U.S. Pat. Nos. 2,267,466 and 2,335,120. Rousch, Jr., U.S. Pat. No. 4,433,629, teaches another solution, with bearing housings which include thereon a lateral thrust absorption pad which is compressed between the bearing housings and the truck frame. The thrust pad acts in compression to absorb the lateral thrust loads and may be easily removed and replaced, since it is entirely external. Each bearing housing includes a pair of stop members thereon which confront the inside of the frame pedestals and are laterally spaced there from by a predetermined amount. Each stop member has mounted thereto a lateral thrust load absorption pad comprised of an elastomer pad bonded to a hardened wear plate. The predetermined clearance between the stop member and the pedestals of the truck frame is sufficient to allow a given amount of unrestricted lateral movement and to allow the elastomer pad to be compressed to absorb the lateral thrust load. Though some lateral movement of the axle and wheel sets relative to the truck frame is necessary to allow the rail truck to properly negotiate a curve, "unrestricted lateral movement" is undesirable due to the increased potential for hunting.
It is therefore an object of the invention to absorb lateral thrust loads between the bearing housings and frame of a rail truck, while at the same time allowing sufficient freedom of lateral movement to permit smooth negotiation of curved track sections.
It is a further object of the present invention to absorb lateral thrust loads between the bearing housings and frame of a rail truck, while at the same time minimizing hunting.
Yet another object of the present invention is to absorb lateral thrust loads between the bearing housings and frame of a rail truck, while at the same time permitting vertical and longitudinal movements of the bearing housings relative to the frame.